FIFA is investigating the 2014 transfer of French international Eliaquim Mangala from FC Porto to Manchester City FC for violation of third-party ownership rules, according to BBC Sport. Mangala joined City for a reported fee of £32m-£42m (€54m, $61m) the BBC report continues. The story was originally reported by Bloomberg Business, BBC Sport states. City is not aware of any investigation and Premier League rules forbid the involvement of third parties in transfers per BBC Sport.

FIFA is investigating the 2014 trade to see if outside investor Doyen Sports played an improper role in negotiating the trade, according to BloombergBusiness. Doyen, which raised 50 million euros as part of its first investment fund, is the biggest investor in the $4 billion transfer market for soccer. It buys a share of the future trade value of a player, betting that whatever he might go for in the future will more than cover the initial investment, the BloombergBusiness report states.

Bloomberg also reports that, in a press release announcing Mangala’s transfer, Porto said it received 30.5 million euros for its 57 percent ownership of Mangala’s contract. Doyen Chief Executive Officer Nelio Lucas said at the time Doyen got a similar valuation for its 33 percent stake, bringing the total fee to about 54 million euros, which is the highest amount ever paid for a defender in the Premier League. The remaining 10 percent stake in Mangala was owned by a London-based company called Robi Plus. Doyen paid Porto 2.6 million euros when it acquired its percentage of Mangala’s transfer rights in 2011.

Doyen is also involved in a case at the Court of Arbitration for Sport with Portugal’s Sporting Lisbon according to the Bloomberg report. The case is centered around Lisbon’s refusal to pay Doyen its portion of the €20m fee for defender Marcos Rojo to Manchester United. Lisbon claims in the Bloomberg report that it was pressured by Doyen to sell Rojo even though they wanted to keep him.

City is not worried about FIFA’s investigation into the transfer of Mangala, according to a report from ESPN FC. Sources close to the story told ESPN FC that City “purchased 100 percent of Mangala’s registration, rather than owning him in conjunction with any third-party” and paid his transfer fee, in full, to Porto and not an agent or an agency.

Mangala said after the move that he was unaware that Doyen and Robi owned almost half of his contract between them, the Manchester Evening Newsstates. Porto could face a fine or a transfer ban if found guilty, after FIFA confirmed to Bloomberg that they are looking into the matter, the Manchester Evening News story continues. Doyen is a group of rich, but anonymous businessmen who speculate on the futures of promising footballers, lending clubs money to buy and taking a stake in the player according to the Manchester Evening News.